The purpose of these studies are to determine what some of the factors are that regulate net prostaglandin E(PGE), PGF, thromboxane A2 (TxA2) and prostacyclin (PGI2) production in the pregnant rat uterus in vivo and to develop a primate model for future work in this area. The first study will determine the levels of (PG's) in vivo in the pregnant rat uterus and uterine venous blood and placenta during the last trimester of pregnancy, and correlate these changes with the gestational alterations in peripheral progesterone, estrone, estradiol-17Beta and pituitary oxytocin (OT). The hormones and PG's will be determined by radioimmunoassay (RIA). The second study wil examine in vivo, the relative contribution of the endometrium and myometrium to PG levels in the pregnant rat uterus. The next set of experiments will determine some of the factors which affect PG levels in the pregnant rat uterus. The effect of progesterone and estradiol-17Beta on uterine PG levels will be examined by ovariectomizing rats at day 19 of pregnancy and placing silastic inserts containing the hormones s.c. and sacrificing the rats 24 hr. later. The local effect of the fetal-placental unit in uterine PG production will be determined by comparing uterine PG concentrations in each horn of unilaterally pregnant rats. The effect of mechanical stretch on uterine PG levels will be studied by removing fetal-placental units and placing paraffin balls of approximate fetal size into the uterus of the treated group of rats. Unilateral pelvic neurectomies (PN) in pregnant rats will be made to study the effect of neural input on PG levels in the uterus. Uterine horns adjacent and opposite the PN will be assayed for PG content and release. The effect of removal of endogenous maternal OT on PG levels in the pregnant rat uterus near or at parturition will be examined by placing transectional surgical "cuts" in the posterior mammillary body region to inhibit the afferent impulses that stimulate OT release. The final objective of these studies is to compare changes in reproductive tissue PG's in the pregnant Baboon at mid (100-103 days) and late (179-182 days) gestation and to correlate the changes with alterations in steroid hormones and maternal and fetal oxytocin.